Genetically modified parthenocarpic eggplants: improved fruit productivity under both greenhouse and open field cultivation

Modulating auxin response stabilizes tomato fruit set

Fruit formation depends on successful fertilization and is highly sensitive to weather fluctuations that affect pollination. Auxin promotes fruit initiation and growth following fertilization. Class A auxin response factors (Class A ARFs) repress transcription in the absence of auxin and activate transcription in its presence. Here, we explore how multiple members of the ARF family regulate fruit set and fruit growth in tomato (Solanum lycopersicum) and Arabidopsis thaliana, and test whether reduction of SlARF activity improves yield stability in fluctuating temperatures. We found that several tomato Slarf mutant combinations produced seedless parthenocarpic fruits, most notably mutants deficient in SlARF8A and SlARF8B genes. Arabidopsis Atarf8 mutants deficient in the orthologous gene had less complete parthenocarpy than did tomato Slarf8a Slarf8b mutants. Conversely, Atarf6 Atarf8 double mutants had reduced fruit growth after fertilization. AtARF6 and AtARF8 likely switch from repression to activation of fruit growth in response to a fertilization-induced auxin increase in gynoecia. Tomato plants with reduced SlARF8A and SlARF8B gene dosage had substantially higher yield than the wild type under controlled or ambient hot and cold growth conditions. In field trials, partial reduction in the SlARF8 dose increased yield under extreme temperature with minimal pleiotropic effects. The stable yield of the mutant plants resulted from a combination of early onset of fruit set, more fruit-bearing branches and more flowers setting fruits. Thus, ARF8 proteins mediate the control of fruit set, and relieving this control with Slarf8 mutations may be utilized in breeding to increase yield stability in tomato and other crops.

Seedlessness Trait and Genome Editing—A Review

Parthenocarpy and stenospermocarpy are the two mechanisms underlying the seedless fruit set program. Seedless fruit occurs naturally and can be produced using hormone application, crossbreeding, or ploidy breeding. However, the two types of breeding are time-consuming and sometimes ineffective due to interspecies hybridization barriers or the absence of appropriate parental genotypes to use in the breeding process. The genetic engineering approach provides a better prospect, which can be explored based on an understanding of the genetic causes underlying the seedlessness trait. For instance, CRISPR/Cas is a comprehensive and precise technology. The prerequisite for using the strategy to induce seedlessness is identifying the crucial master gene or transcription factor liable for seed formation/development. In this review, we primarily explored the seedlessness mechanisms and identified the potential candidate genes underlying seed development. We also discussed the CRISPR/Cas-mediated genome editing approaches and their improvements.

A Compendium for Novel Marker-Based Breeding Strategies in Eggplant

The worldwide production of eggplant is estimated at about 58 Mt, with China, India and Egypt being the major producing countries. Breeding efforts in the species have mainly focused on increasing productivity, abiotic and biotic tolerance/resistance, shelf-life, the content of health-promoting metabolites in the fruit rather than decreasing the content of anti-nutritional compounds in the fruit. From the literature, we collected information on mapping quantitative trait loci (QTLs) affecting eggplant's traits following a biparental or multi-parent approach as well as genome-wide association (GWA) studies. The positions of QTLs were lifted according to the eggplant reference line (v4.1) and more than 700 QTLs were identified, here organized into 180 quantitative genomic regions (QGRs). Our findings thus provide a tool to: (i) determine the best donor genotypes for specific traits; (ii) narrow down QTL regions affecting a trait by combining information from different populations; (iii) pinpoint potential candidate genes.

A Flashforward Look into Solutions for Fruit and Vegetable Production

One of the most important challenges facing current and future generations is how climate change and continuous population growth adversely affect food security. To address this, the food system needs a complete transformation where more is produced in non-optimal and space-limited areas while reducing negative environmental impacts. Fruits and vegetables, essential for human health, are high-value-added crops, which are grown in both greenhouses and open field environments. Here, we review potential practices to reduce the impact of climate variation and ecosystem damages on fruit and vegetable crop yield, as well as highlight current bottlenecks for indoor and outdoor agrosystems. To obtain sustainability, high-tech greenhouses are increasingly important and biotechnological means are becoming instrumental in designing the crops of tomorrow. We discuss key traits that need to be studied to improve agrosystem sustainability and fruit yield.

Positive effects of applying endophytic bacteria in eggplant-Sedum intercropping system on Cd phytoremediation and vegetable production in cadmium polluted greenhouse

The combination of intercropping and phytoremediation in the remediation of cadmium contaminated soil is an emerging model in recent years, but the results of previous studies are inconsistent. In the field experiment, eggplant was intercropped with hyperaccumulator Sedum alfredii Hance (inoculated or not inoculated with endophytic bacteria) to study the effects of intercropping on vegetable safety production, phytoremediation efficiency of hyperaccumulator and variation of soil available nutrients. The results showed that the intercropping treatment had a negative effect on the growth of eggplant and Sedum, but endophyte SaMR12 alleviated the inhibition of intercropping on plant growth. Intercropping treatment increases the Cd concentration in edible part of eggplant to 1.34 mg/kg compared with eggplant monoculture (1.19 mg/kg). While the application of SaMR12 reduces the Cd concentration of eggplant fruit to 0.95 mg/kg and significantly promotes the Cd uptake by Sedum. What's more surprising is that compared with eggplant monocropping, the content of soil available nitrogen, phosphorus and potassium in the treatment of intercropping with inoculated Sedum increased significantly. And according to the correlation analysis of various indexes of plants and soil, the Cd content of eggplant is negatively correlated with the available phosphorus and potassium in the soil, while the Cd content of Sedum is positively correlated with it, which suggested that the application of phosphorus and potassium fertilizers in this experimental site was beneficial to reduce Cd content in eggplant and improve Cd phytoextraction of Sedum. Therefore, in the daily production of moderately Cd-contaminated soil, intercropping eggplant with Sedum inoculated with endophytic bacteria is an excellent Phytoextraction Coupled with Agro-safe-production (PCA) pattern.

Transcriptomic, Hormonomic and Metabolomic Analyses Highlighted the Common Modules Related to Photosynthesis, Sugar Metabolism and Cell Division in Parthenocarpic Tomato Fruits during Early Fruit Set

Parthenocarpy, the pollination-independent fruit set, can raise the productivity of the fruit set even under adverse factors during the reproductive phase. The application of plant hormones stimulates parthenocarpy, but artificial hormones incur extra financial and labour costs to farmers and can induce the formation of deformed fruit. This study examines the performance of parthenocarpic mutants having no transcription factors of SlIAA9 and SlTAP3 and sldella that do not have the protein-coding gene, SlDELLA, in tomato (cv. Micro-Tom). At 0 day after the flowering (DAF) stage and DAFs after pollination, the sliaa9 mutant demonstrated increased pistil development compared to the other two mutants and wild type (WT). In contrast to WT and the other mutants, the sliaa9 mutant with pollination efficiently stimulated the build-up of auxin and GAs after flowering. Alterations in both transcript and metabolite profiles existed for WT with and without pollination, while the three mutants without pollination demonstrated the comparable metabolomic status of pollinated WT. Network analysis showed key modules linked to photosynthesis, sugar metabolism and cell proliferation. Equivalent modules were noticed in the famous parthenocarpic cultivars ‘Severianin’, particularly for emasculated samples. Our discovery indicates that controlling the genes and metabolites proffers future breeding policies for tomatoes.

Accumulation of the Auxin Precursor Indole-3-Acetamide Curtails Growth through the Repression of Ribosome-Biogenesis and Development-Related Transcriptional Networks

The major auxin, indole-3-acetic acid (IAA), is associated with a plethora of growth and developmental processes including embryo development, expansion growth, cambial activity, and the induction of lateral root growth. Accumulation of the auxin precursor indole-3-acetamide (IAM) induces stress related processes by stimulating abscisic acid (ABA) biosynthesis. How IAM signaling is controlled is, at present, unclear. Here, we characterize the ami1rooty double mutant, that we initially generated to study the metabolic and phenotypic consequences of a simultaneous genetic blockade of the indole glucosinolate and IAM pathways in Arabidopsisthaliana. Our mass spectrometric analyses of the mutant revealed that the combination of the two mutations is not sufficient to fully prevent the conversion of IAM to IAA. The detected strong accumulation of IAM was, however, recognized to substantially impair seed development. We further show by genome-wide expression studies that the double mutant is broadly affected in its translational capacity, and that a small number of plant growth regulating transcriptional circuits are repressed by the high IAM content in the seed. In accordance with the previously described growth reduction in response to elevated IAM levels, our data support the hypothesis that IAM is a growth repressing counterpart to IAA.

CPPU may induce gibberellin-independent parthenocarpy associated with PbRR9 in 'Dangshansu' pear

Parthenocarpy is a valuable trait in self-incompatible plants, such as pear. N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU), a synthetic cytokinin analog, can induce parthenocarpy in pear (Pyrus spp.), but the mechanism of induction is unclear. To investigate the role of gibberellin in CPPU-induced parthenocarpy in pear, CPPU supplemented with paclobutrazol (PAC) was sprayed onto 'Dangshansu' pear. We found that the fruit set rate of pear treated with CPPU supplemented with PAC was identical to that in a CPPU-alone treatment group. In regard to cell development, CPPU mainly promoted hypanthium cell division and expansion, and PAC application had no influence on CPPU-induced cell development. RNA sequencing revealed that gibberellin 20 oxidase and gibberellin 3 oxidase genes were not differentially expressed following CPPU treatment. According to the analysis of fruit phytohormone content, the CPPU treatments did not induce gibberellin biosynthesis. These results suggest that CPPU-induced parthenocarpy may be gibberellin independent in 'Dangshansu' pear. After CPPU treatment, the indole acetic acid (IAA) content in fruit was significantly increased, and the abscisic acid (ABA) content was significantly decreased. Similarly, RNA sequencing revealed that many genes involved in the auxin and ABA pathways were significantly differentially expressed in the CPPU treatment groups; among them, indole-3-pyruvate monooxygenase (YUCCA) was significantly upregulated and 9-cis-epoxycarotenoid dioxygenase (NCED) was significantly downregulated. IAA and ABA may thus play important roles in CPPU-induced parthenocarpy. PbTwo-component response regulator9 (PbRR9), PbYUCCA4, and PbNCED6 were then selected to further elucidate the mechanism of CPPU-induced parthenocarpy. A yeast one-hybrid assay indicated that PbRR9 can combine with the PbYUCCA4 and PbNCED6 promoters. Dual luciferase assays revealed that PbRR9 can promote and repress the activities of the PbYUCCA4 and PbNCED6 promoters, respectively. After the transient expression of PbRR9 in fruits, PbYUCCA4 expression was significantly upregulated, and PbNCED6 expression was significantly downregulated. This study uncovered a CPPU-induced parthenocarpy mechanism that is different from that in tomato. CPPU may upregulate PbYUCCA4 and downregulate PbNCED6 by upregulating PbRR9, thereby increasing IAA content and decreasing ABA content to ultimately induce parthenocarpy in 'Dangshansu' pear. However, because only a single time point was used and because 'botanical' and 'accessory' fruits have different structures, this conclusion is still preliminary.

Fruit ripening: the role of hormones, cell wall modifications, and their relationship with pathogens

Fruits result from complex biological processes that begin soon after fertilization. Among these processes are cell division and expansion, accumulation of secondary metabolites, and an increase in carbohydrate biosynthesis. Later fruit ripening is accomplished by chlorophyll degradation and cell wall lysis. Fruit maturation is an essential step to optimize seed dispersal, and is controlled by a complex network of transcription factors and genetic regulators that are strongly influenced by phytohormones. Abscisic acid (ABA) and ethylene are the major regulators of ripening and senescence in both dry and fleshy fruits, as demonstrated by numerous ripening-defective mutants, effects of exogenous hormone application, and transcriptome analyses. While ethylene is the best characterized player in the final step of a fruit's life, ABA also has a key regulatory role, promoting ethylene production and acting as a stress-related hormone in response to drought and pathogen attack. In this review, we focus on the role of ABA and ethylene in relation to the interconnected biotic and abiotic phenomena that affect ripening and senescence. We integrate and discuss the most recent data available regarding these biological processes, which are crucial for post-harvest fruit conservation and for food safety.

Transcriptome analysis of oil palm inflorescences revealed candidate genes for an auxin signaling pathway involved in parthenocarpy

Oil palm parthenocarpic fruits, which are produced without fertilization, can be targeted to increase oil content because the majority of the fruit is occupied by mesocarp, the part in which palm oil is stored. Consequently, gaining an understanding of the parthenocarpic mechanism would be instrumental for producing parthenocarpic oil palm. This study aims to determine effects of auxin treatment and analyze differentially expressed genes in oil palm pistils at the pollination/anthesis stage, using an RNA sequencing (RNA seq) approach. The auxin treatment caused 100% parthenocarpy when auxin was sprayed before stigmas opened. The parthenocarpy decreased to 55%, 8% and 5% when the auxin was sprayed 1, 2 and 3 days after the opening of stigmas, respectively. Oil palm plants used for RNA seq were plants untreated with auxin as controls and auxin-treated plants on the day before pollination and 1 day after pollination. The number of raw reads ranged from 8,425,859 to 11,811,166 reads, with an average size ranging from 99 to 137 base pairs (bp). When compared with the oil palm transcriptome, the mapped reads ranged from 8,179,948 to 11,320,799 reads, representing 95.85–98.01% of the oil palm matching. Based on five comparisons between RNA seq of treatments and controls, and confirmation using reverse transcription polymerase chain reaction and quantitative real-time RT-PCR expression, five candidate genes, including probable indole-3-acetic acid (IAA)-amido synthetase GH3.8 (EgGH3.8), IAA-amido synthetase GH3.1 (EgGH3.1), IAA induced ARG7 like (EgARG7), tryptophan amino transferase-related protein 3-like (EgTAA3) and flavin-containing monooxygenase 1 (EgFMO1), were differentially expressed between auxin-treated and untreated samples. This evidence suggests a pathway of parthenocarpic fruit development at the beginning of fruit development. However, more research is needed to identify which genes are definitely involved in parthenocarpy.

Genetic Engineering: A Possible Strategy for Protein-Energy Malnutrition Regulation

Protein-energy malnutrition (PEM) has adversely affected the generations of developing countries. It is a syndrome that in severity causes death. PEM generally affects infants of 1-5 age group. This manifestation is maintained till adulthood in the form of poor brain and body development. The developing nations are continuously making an effort to curb PEM. However, it is still a prime concern as it was in its early years of occurrence. Transgenic crops with high protein and enhanced nutrient content have been successfully developed. Present article reviews the studies documenting genetic engineering-mediated improvement in the pulses, cereals, legumes, fruits and other crop plants in terms of nutritional value, stress tolerance, longevity and productivity. Such genetically engineered crops can be used as a possible remedial tool to eradicate PEM.

Comparative transcriptome analysis provides insights into molecular mechanisms for parthenocarpic fruit development in eggplant (Solanum melongena L.)

Genetic control of parthenocarpy, a desirable trait in edible fruit with hard seeds, has been extensively studied. However, the molecular mechanism of parthenocarpic fruit development in eggplant (Solanum melongena L.) is still unclear. To provide insights into eggplant parthenocarpy, the transcriptomic profiles of a natural parthenocarpic (PP05) and two non-parthenocarpic (PnP05 and GnP05) eggplant lines were analyzed using RNA-sequencing (RNA-seq) technology. These sequences were assembled into 38925 unigenes, of which 22683 had an annotated function and 3419 were predicted as novel genes or from alternative splicing. 4864 and 1592 unigenes that were identified as DEGs between comparison groups PP05 vs PnP05 and PP05 vs GnP05, respectively. 506 common DEGs were found contained in both comparison groups, including 258 up-regulated and 248 down-regulated genes. Functional enrichment analyses identified many common or specific biological processes and gene set potentially associated with plant development. The most pronounced findings are that differentially regulated genes potentially-related with auxin signaling between parthenocarpic and non-parthenocarpic eggplants, e.g. calcium-binding protein PBP1 and transcription factor E2FB, which mediate the auxin distribution and auxin-dependent cell division, respectively, are up-regulated in the PP05; whereas homologs of GH3.1 and AUX/IAA, which are involved in inactivation of IAA and interference of auxin signaling, respectively, are down-regulated in PP05. Furthermore, gibberellin and cytokinin signaling genes and genes related to flower development were found differentially regulated between these eggplant lines. The present study provides comprehensive transcriptomic profiles of eggplants with or without parthenocarpic capacity. The information will deepen our understanding of the molecular mechanisms of eggplant parthenocarpy. The DEGs, especially these filtered from PP05 vs PnP05 + GnP05, will be valuable for further investigation of key genes involved in the parthenocarpic fruit development and genomics-assisted breeding.

Comparative transcriptome analysis during early fruit development between three seedy citrus genotypes and their seedless mutants

Identification of genes with differential transcript abundance (GDTA) in seedless mutants may enhance understanding of seedless citrus development. Transcriptome analysis was conducted at three time points during early fruit development (Phase 1) of three seedy citrus genotypes: Fallglo (Bower citrus hybrid (Citrus reticulata×C. reticulata×C. paradisi)×Temple (C. reticulata×C. sinensis)), grapefruit (C. paradisi), Pineapple sweet orange (C. sinensis), and their seedless mutants. Seed abortion in seedless mutants was observed at 26 days post anthesis (Time point 2). Affymetrix transcriptomic analysis revealed 359 to 1077 probe sets with differential transcript abundance in the comparison of seedless versus seedy fruits for each citrus genotypes and time points. The GDTA identified by 18 microarray probe sets were validated by qPCR. Hierarchical clustering analysis revealed a range of GDTA associated with development, hormone and protein metabolism, all of which may reflect genes associated with seedless fruit development. There were 14, 9 and 12 genes found exhibiting similar abundance ratios in all three seedless versus seedy genotype comparisons at time point 1, 2 and 3, respectively. Among those genes were genes coding for an aspartic protease and a cysteine protease, which may play important roles in seedless fruit development. New insights into seedless citrus fruit development may contribute to biotech approaches to create seedless cultivars.

Re-evaluating strategies for pollinator-dependent crops: How useful is parthenocarpy?

Whilst most studies reviewing the reliance of global agriculture on insect pollination advocate increasing the ‘supply’ of pollinators (wild or managed) to improve crop yields, there has been little focus on altering a crop's ‘demand’ for pollinators.

Parthenocarpy (fruit set in the absence of fertilization) is a trait which can increase fruit quantity and quality from pollinator‐dependent crops by removing the need for pollination.

Here we present a meta‐analysis of studies examining the extent and effectiveness of parthenocarpy‐promoting techniques (genetic modification, hormone application and selective breeding) currently being used commercially, or experimentally, on pollinator‐dependent crops in different test environments (no pollination, hand pollination, open pollination).

All techniques significantly increased fruit quantity and quality in 18 pollinator‐dependent crop species (not including seed and nut crops as parthenocarpy causes seedlessness). The degree to which plants experienced pollen limitation in the different test environments could not be ascertained, so the absolute effect of parthenocarpy relative to optimal pollination could not be determined.

Synthesis and applications. Parthenocarpy has the potential to lower a crop's demand for pollinators, whilst extending current geographic and climatic ranges of production. Thus, growers may wish to use parthenocarpic crop plants, in combination with other environmentally considerate practices, to improve food security and their economic prospects.

Parthenocarpy has the potential to lower a crop's demand for pollinators, whilst extending current geographic and climatic ranges of production. Thus, growers may wish to use parthenocarpic crop plants, in combination with other environmentally considerate practices, to improve food security and their economic prospects.

Heterologous expression of Arabidopsis C-repeat binding factor 3 (AtCBF3) and cold-regulated 15A (AtCOR15A) enhanced chilling tolerance in transgenic eggplant (Solanum melongena L.)

Our study shows that the expression of AtCBF3 and AtCOR15A improved the chilling tolerance in transgenic eggplant. In an attempt to improve chilling tolerance of eggplant (Solanum melongena L) plants, Arabidopsis C-repeat binding factor 3 (AtCBF3) and cold-regulated 15A (AtCOR15A) genes both driven by an Arabidopsis RESPONSIVE TO DESSICATION 29A promoter (AtRD29A) were transferred into the plants of eggplant cultivar Sanyueqie. Two independent homozygous transgenic lines were tested for their cold tolerance. The leaves of the transgenic plants in both lines withered much slower and slighter than the wild-type plants after exposure to cold stress treatment at 2 ± 1 °C. The gene expression of AtCBF3 and AtCOR15A was significantly increased as well as the proline content and the levels of catalase and peroxidase activities, while the relative electrical conductivity and the malondialdehyde content were remarkably decreased in the transgenic plants compared with the wild type at 4 ± 0.5 °C. The results showed that the expression of the exogenous AtCBF3 and AtCOR15A could promote the cold adaptation process to protect eggplant plants from chilling stress.

Transcriptome comparison of global distinctive features between pollination and parthenocarpic fruit set reveals transcriptional phytohormone cross-talk in cucumber (Cucumis sativus L.)

Parthenocarpy is an important trait determining yield and quality of fruit crops. However, the understanding of the mechanisms underlying parthenocarpy induction is limited. Cucumber (Cucumis sativus L.) is abundant in parthenocarpic germplasm resources and is an excellent model organism for parthenocarpy studies. In this study, the transcriptome of cucumber fruits was studied using RNA sequencing (RNA-Seq). Differentially expressed genes (DEGs) of set fruits were compared against aborted fruits. Distinctive features of parthenocarpic and pollinated fruits were revealed by combining the analysis of the transcriptome together with cytomorphological and physiological analysis. Cell division and the transcription of cell division genes were found to be more active in parthenocarpic fruit. The study also indicated that parthenocarpic fruit set is a high sugar-consuming process which is achieved via enhanced carbohydrate degradation through transcription of genes that lead to the breakdown of carbohydrates. Furthermore, the evidence provided by this work supports a hypothesis that parthenocarpic fruit set is induced by mimicking the processes of pollination/fertilization at the transcriptional level, i.e. by performing the same transcriptional patterns of genes inducing pollination and gametophyte development as in pollinated fruit. Based on the RNA-Seq and ovary transient expression results, 14 genes were predicted as putative parthenocarpic genes. The transcription analysis of these candidate genes revealed auxin, cytokinin and gibberellin cross-talk at the transcriptional level during parthenocarpic fruit set.

Mechanisms regulating auxin action during fruit development

Auxin controls many aspects of fruit development, including fruit set and growth, ripening and abscission. However, the mechanisms by which auxin regulates these processes are still poorly understood. While it is generally agreed that precise spatial and temporal control of auxin distribution and signaling are required for fruit development, the dynamics of auxin biosynthesis and the mechanisms for its transport to different fruit tissues are mostly unknown. Despite major advances in elucidating many aspects of auxin biology in vegetative tissues, until recently, the nature and importance of auxin metabolism, transport and signaling during fruit ontogeny remained obscure. In this review, we summarize recent research that has started to elucidate the molecular mechanisms by which auxin is produced and transported in the fruit and to unravel the complexity of auxin signaling during fruit development. We also discuss recent approaches used to reveal the genes and regulatory networks that mediate cell and tissue-specific control of auxin levels in the developing fruit.

Vigor for in vitro culture traits in S. melongena × S. aethiopicum hybrids with potential as rootstocks for eggplant

Hybrids of Solanum melongena and S. aethiopicum are of interest as rootstocks of eggplant, as they are highly vigorous and can incorporate resistance to several diseases. However, hybridization between both species is difficult. Therefore, protocols for in vitro culture are of great interest for their micropropagation and biotechnological breeding. We assessed the organogenesis response from leaf explants in four interspecific hybrids and in their parents testing two organogenic media: SIM-A, containing 6-benzylaminopurine and kinetin, and SIM-B, which contains thidiazuron. A higher regeneration capacity in the hybrids compared to their parents was observed. Whereas in interspecific hybrids and in one accession of S. melongena similar regeneration rates were observed for SIM-A and SIM-B, higher regeneration was found in the rest of genotypes when thidiazuron was used. Rooting ability in the interspecific hybrids was lower in in vitro micropropagated plants (35-60%) than in plants regenerated from explants (100%). The addition of indolbutiric acid (1 mg L(-1)) induced roots in nonrooted genotypes. In summary, we have adjusted in vitro culture conditions for regenerating and rooting S. melongena × S. aethiopicum hybrids. We have also demonstrated that these hybrids are heterotic for regeneration, which may be of interest for basic science studies.

Development of selective markers linked to a major QTL for parthenocarpy in eggplant (Solanum melongena L.)

Parthenocarpy, the ability to set fruits without pollination, is a useful trait for setting fruit under unfavorable conditions. To identify the loci controlling parthenocarpy in eggplant (Solanum melongena L.), we constructed linkage maps by using co-dominant simple sequence repeat and single nucleotide polymorphism markers in F(2) populations derived from intraspecific crosses between two non-parthenocarpic lines (LS1934 and Nakate-Shinkuro) and a parthenocarpic line (AE-P03). Total map distances were 1,414.6 cM (ALF2: LS1934 x AE-P03) and 1,153.8 cM (NAF2: Nakate-Shinkuro x AE-P03), respectively. Quantitative trait locus (QTL) analyses revealed two QTLs on chromosomes 3 and 8, which we denoted as Controlling parthenocarpy3.1 (Cop3.1) and Cop8.1, respectively. The percentage of phenotypic variance explained (PVE) of Cop3.1 was 6.3% in ALF2 (LOD = 4.2) and 10.6% in NAF2 (LOD = 3.0). The PVE of Cop8.1 was 45.7% in ALF2 (LOD = 23.8) and 29.7% in NAF2 (LOD = 7.9). Using a population of backcross inbred lines, we confirmed the effect of Cop8.1, but there was no evidence to support the contribution of Cop3.1. We need to verify the effect of Cop3.1 under various temperature conditions. In addition, we clarified the effectiveness of selective SSR markers, emf21H22 and emh11J10, mapped on each side of Cop8.1 in other F(2) populations derived from various parental combinations. This is the first report concerning QTL analysis of parthenocarpy in eggplant using molecular markers. It will be useful in marker-assisted selection and in revealing the genomic mechanism underlying parthenocarpy in eggplant.

Over-expression of a grape stilbene synthase gene in tomato induces parthenocarpy and causes abnormal pollen development

A novel strategy to induce parthenocarpy in tomato fruits by the induction of resveratrol biosynthesis in flower tissues was exploited. Two transgenic tomato lines were considered: a higher resveratrol-producing (35SS) line, constitutively expressing a grape stilbene synthase cDNA, and a lower resveratrol-producing (LoxS) line, expressing stilbene synthase under a fruit-specific promoter. The expression of the stilbene synthase gene affected flavonoid metabolism in a different manner in the transgenic lines, and in one of these, the 35SS line, resulted in complete male sterility. Resveratrol was synthesised either in 35SS or LoxS tomato flowers, at an even higher extent (about 8-10 times) in the former line. We further investigated whether stilbene synthase expression may have resulted in impaired naringenin accumulation during flower development. In the 35SS flowers, naringenin was significantly impaired by about 50%, probably due to metabolic competition. Conversely, the amount of glycosylated flavonols increased in transgenic flowers, thereby excluding the diminished production of flavonols as a reason for parthenocarpy in tomato. We further investigated whether resveratrol synthesis may have resulted changes to pollen structure. Microscopic observations revealed the presence of few and abnormal flake-like pollen grains in 35SS flowers with no germination capability. Finally, the analysis of coumaric and ferulic acids, the precursors of lignin and sporopollenin biosynthesis, revealed significant depletion of these compounds, therefore suggesting an impairment in structural compounds as a reason for pollen ablation. These overall outcomes, to the best of our knowledge, reveal for the first time the major role displayed by resveratrol synthesis on parthenocarpy in tomato fruits.

Unsupervised principal component analysis of NMR metabolic profiles for the assessment of substantial equivalence of transgenic grapes (Vitis vinifera)

Substantial equivalence is a key concept in the evaluation of unintended and potentially harmful metabolic impact consequent to a genetic modification of food. The application of unsupervised multivariate data analysis to the metabolic profiles is expected to improve the effectiveness of such evaluation. The present study uses NMR spectra of hydroalcoholic extracts, as holistic representations of the metabolic profiles of grapes, to evaluate the effect of the insertion of one or three copies of the DefH9-iaaM construct in plants of Silcora and Thompson Seedless cultivars. The comparison of the metabolic profiles of transgenic derivatives with respect to their corresponding natural lines pointed out that the overall metabolic changes occur in the same direction, independent of the host genotype, although the two cultivars are modified to different extents. A higher number of copies not only produces a larger effect but also modifies the whole pattern of perturbed metabolites.

Greenhouse and field cultivations of antigen-expressing potatoes focusing on the variability in plant constituents and antigen expression

The production of plant-derived pharmaceuticals essentially requires stable concentrations of plant constituents, especially recombinant proteins; nonetheless, soil and seasonal variations might drastically interfere with this stability. In addition, variability might depend on the plant organ used for production. Therefore, we investigated the variability in plant constituents and antigen expression in potato plants under greenhouse and field growth conditions and in leaves compared to tubers. Using potatoes expressing VP60, the only structural capsid protein of the rabbit haemorrhagic disease virus (RHDV), CTB, the non-toxic B subunit (CTB) of the cholera toxin (CTA-CTB(5)) and the marker protein NPTII (neomycinphosphotransferase) as a model, we compare greenhouse and field production of potato-derived antigens. The influence of the production organ turned out to be transgene specific. In general, yield, plant quality and transgene expression levels in the field were higher than or similar to those observed in the greenhouse. The variation (CV) of major plant constituents and the amount of transgene-encoded protein was not influenced by the higher variation of soil properties observed in the field. Amazingly, for specific events, the variability in the model protein concentrations was often lower under field than under greenhouse conditions. The changes in gene expression under environmental stress conditions in the field observed in another event do not reduce the positive influence on variability since events like these should excluded from production. Hence, it can be concluded that for specific applications, field production of transgenic plants producing pharmaceuticals is superior to greenhouse production, even concerning the stability of transgene expression over different years. On the basis of our results, we expect equal or even higher expression levels with lower variability of recombinant pharmaceuticals in the field compared to greenhouse production combined with approximately 10 times higher tuber yield in the field.

Seedless fruit production by hormonal regulation of fruit set

Seed and fruit development are intimately related processes controlled by internal signals and environmental cues. The absence of seeds is usually appreciated by consumers and producers because it increases fruit quality and fruit shelf-life. One method to produce seedless fruit is to develop plants able to produce fruits independently from pollination and fertilization of the ovules. The onset of fruit growth is under the control of phytohormones. Recent genomic studies have greatly contributed to elucidate the role of phytohormones in regulating fruit initiation, providing at the same time genetic methods for introducing seedlessness in horticultural plants.

Gene regulation in parthenocarpic tomato fruit

Parthenocarpy is potentially a desirable trait for many commercially grown fruits if undesirable changes to structure, flavour, or nutrition can be avoided. Parthenocarpic transgenic tomato plants (cv MicroTom) were obtained by the regulation of genes for auxin synthesis (iaaM) or responsiveness (rolB) driven by DefH9 or the INNER NO OUTER (INO) promoter from Arabidopsis thaliana. Fruits at a breaker stage were analysed at a transcriptomic and metabolomic level using microarrays, real-time reverse transcription-polymerase chain reaction (RT-PCR) and a Pegasus III TOF (time of flight) mass spectrometer. Although differences were observed in the shape of fully ripe fruits, no clear correlation could be made between the number of seeds, transgene, and fruit size. Expression of auxin synthesis or responsiveness genes by both of these promoters produced seedless parthenocarpic fruits. Eighty-three percent of the genes measured showed no significant differences in expression due to parthenocarpy. The remaining 17% with significant variation (P <0.05) (1748 genes) were studied by assigning a predicted function (when known) based on BLAST to the TAIR database. Among them several genes belong to cell wall, hormone metabolism and response (auxin in particular), and metabolism of sugars and lipids. Up-regulation of lipid transfer proteins and differential expression of several indole-3-acetic acid (IAA)- and ethylene-associated genes were observed in transgenic parthenocarpic fruits. Despite differences in several fatty acids, amino acids, and other metabolites, the fundamental metabolic profile remains unchanged. This work showed that parthenocarpy with ovule-specific alteration of auxin synthesis or response driven by the INO promoter could be effectively applied where such changes are commercially desirable.

Auxin synthesis-encoding transgene enhances grape fecundity

Grape (Vitis vinifera) yield is largely dependent on the fecundity of the cultivar. The average number of inflorescences per shoot (i.e. shoot fruitfulness) is a trait related to fecundity of each grapevine. Berry number and weight per bunch are other features affecting grape yield. An ovule-specific auxin-synthesizing (DefH9-iaaM) transgene that increases the indole-3-acetic acid content of grape transgenic berries was transformed into cultivars Silcora and Thompson Seedless, which differ in the average number of inflorescences per shoots. Thompson Seedless naturally has very low shoot fruitfulness, whereas Silcora has medium shoot fruitfulness. The average number of inflorescences per shoot in DefH9-iaaM Thompson Seedless was doubled compared to its wild-type control. Berry number per bunch was increased in both transgenic cultivars. The quality and nutritional value of transgenic berries were substantially equivalent to their control fruits. The data presented indicate that auxin enhances fecundity in grapes, thus enabling to increase yield with lower production costs.

Open field trial of genetically modified parthenocarpic tomato: seedlessness and fruit quality

Background

Parthenocarpic tomato lines transgenic for the DefH9-RI-iaaM gene have been cultivated under open field conditions to address some aspects of the equivalence of genetically modified (GM) fruit in comparison to controls (non-GM).

Results

Under open field cultivation conditions, two tomato lines (UC 82) transgenic for the DefH9-RI-iaaM gene produced parthenocarpic fruits. DefH9-RI-iaaM fruits were either seedless or contained very few seeds. GM fruit quality, with the exception of a higher β-carotene level, did not show any difference, neither technological (colour, firmness, dry matter, °Brix, pH) nor chemical (titratable acidity, organic acids, lycopene, tomatine, total polyphenols and antioxidant capacity – TEAC), when compared to that of fruits from control line. Highly significant differences in quality traits exist between the tomato F1 commercial hybrid Allflesh and the three UC 82 genotypes tested, regardless of whether or not they are GM. Total yield per plant did not differ between GM and parental line UC 82. Fruit number was increased in GM lines, and GM fruit weight was decreased.

Conclusion

The use in the diet of fruits from a new line or variety introduces much greater changes than the consumption of GM fruits in comparison to its genetic background. Parthenocarpic fruits, produced under open field conditions, contained 10-fold less seeds than control fruits. Thus parthenocarpy caused by DefH9-RI-iaaM gene represents also a tool for mitigating GM seeds dispersal in the environment.

Parthenocarpic fruit development in tomato

Parthenocarpic fruit development is a very attractive trait for growers and consumers. In tomato, three main sources of facultative parthenocarpy, pat, pat-2, pat-3/pat-4, are known to have potential applications in agriculture. The parthenocarpic fruit development in these lines is triggered by a deregulation of the hormonal balance in some specific tissues. Auxins and gibberellins are considered as the key elements in parthenocarpic fruit development of those lines. An increased level of these hormones in the ovary can substitute for pollination and trigger fruit development. This has opened up genetic engineering approaches for parthenocarpy that have given promising results, both in quality and quantity of seedless fruit production.

The defH9-iaaM auxin-synthesizing gene increases plant fecundity and fruit production in strawberry and raspberry

Background

The DefH9-iaaM gene fusion which is expressed specifically in placenta/ovules and promotes auxin-synthesis confers parthenocarpic fruit development to eggplant, tomato and tobacco. Transgenic DefH9-iaaM eggplants and tomatoes show increased fruit production due mainly to an improved fruit set. However, the weight of the fruits is also frequently increased.

Results

DefH9-iaaM strawberry and raspberry plants grown under standard cultivation conditions show a significant increase in fruit number and size and fruit yield. In all three Rosaceae species tested, Fragaria vesca, Fragaria x ananassa and Rubus idaeus, DefH9-iaaM plants have an increased number of flowers per inflorescence and an increased number of inflorescences per plant. This results in an increased number of fruits per plant. Moreover, the weight and size of transgenic fruits was also increased. The increase in fruit yield was approximately 180% in cultivated strawberry, 140% in wild strawberry, and 100% in raspberry. The DefH9-iaaM gene is expressed in the flower buds of all three species. The total IAA (auxin) content of young flower buds of strawberry and raspberry expressing the DefH9-iaaM gene is increased in comparison to untransformed flower buds. The DefH9-iaaM gene promotes parthenocarpy in emasculated flowers of both strawberry and raspberry.

Conclusions

The DefH9-iaaM gene is expressed and biologically active in Rosaceae. The DefH9-iaaM gene can be used, under cultivation conditions that allow pollination and fertilization, to increase fruit productivity significantly in Rosaceae species. The finding that the DefH9-iaaM auxin-synthesizing gene increases the number of inflorescences per plant and the number of flowers per inflorescence indicates that auxin plays a role in plant fecundity in these three perennial Rosaceae species.

Genetic transformation of Vitis vinifera via organogenesis

BACKGROUND

Efficient transformation and regeneration methods are a priority for successful application of genetic engineering to vegetative propagated plants such as grape. The current methods for the production of transgenic grape plants are based on Agrobacterium-mediated transformation followed by regeneration from embryogenic callus. However, grape embryogenic calli are laborious to establish and the phenotype of the regenerated plants can be altered.

RESULTS

Transgenic grape plants (V. vinifera, table-grape cultivars Silcora and Thompson Seedless) were produced using a method based on regeneration via organogenesis. In vitro proliferating shoots were cultured in the presence of increasing concentrations of N6-benzyl adenine. The apical dome of the shoot was removed at each transplantation which, after three months, produced meristematic bulk tissue characterized by a strong capacity to differentiate adventitious shoots. Slices prepared from the meristematic bulk were used for Agrobacterium-mediated transformation of grape plants with the gene DefH9-iaaM. After rooting on kanamycin containing media and greenhouse acclimatization, transgenic plants were transferred to the field. At the end of the first year of field cultivation, DefH9-iaaM grape plants were phenotypically homogeneous and did not show any morphological alterations in vegetative growth. The expression of DefH9-iaaM gene was detected in transgenic flower buds of both cultivars.

CONCLUSIONS

The phenotypic homogeneity of the regenerated plants highlights the validity of this method for both propagation and genetic transformation of table grape cultivars. Expression of the DefH9-iaaM gene takes place in young flower buds of transgenic plants from both grape cultivars.